The present invention relates to inspecting systems, and more particularly to automatic inspecting systems which enable the visual identification of inspected item characteristics at various positions on an item.
In the prior art there are known a variety of inspection systems which are used in electronics as well as other industries for enabling the inspection of products. In the electronic industry, such devices are particularly used to aid in the identification of defects in electronic circuit boards or aid in the identification of other characteristics which may be undesirable in circuit board construction. As will be apparent, identification of the defects is important in preventing the sale of faulty boards as well as in enabling their repair to reduce waste in the manufacturing process. Because of the nature of the defects which can occur, many systems are specifically tailored to the particular device to be inspected and are thus limited in their application and ease of use in many environments.
One type of inspection that has been used throughout the industry is visual inspection of the item itself. In its basic approach, such systems rely on the visual observation by a human operator of an item and a verbal or written description of the location of any fault or defect which may be observed. More sophisticated systems have employed an automated procedure wherein the position of the item relative to a specific point of observation can be automatically recorded and identified for subsequent replacement or repair of parts or correction of the defect. In one such system, a microprocessor is coupled to a cathode ray tube (CRT) and to a mounting system which includes a two-dimensional sonic digitizer. The circuit board is mounted with respect to the sonic digitizer so that the X-Y coordinates of components or joints in a plane of inspection can be viewed and identified by the operator through a microscope. Inspection is performed by prompting programs displayed on the CRT so that as the positions of defects are identified by the sonic digitizers in response to visual observation, the position of the defects as well as any necessary repair can be correlated automatically by the programming. In this system, however, for the inspection to be successful, the circuit boards must be held at right angles relative to the microscope or direction of viewing in order for the X-Y coordinates to be accurately obtained.
In more complicated systems, visual observation is eliminated by the implementation of a completely automatic system. In one such system, the solder joints of a circuit board are analyzed by indexing an ultrasonic probe to contact each solder joint. When in contact with the joint, the probe is excited and the response of the joint to the probe is analyzed in a programmed microprocessor. The system is restricted to the analysis of the particular circuit board configurations and is generally cumbersome in operation.
In another automatic inspection system, a raster scanning laser is used to heat each solder joint with the laser for a specified time period as the laser scans from joint to joint. An infrared scanner is used in connection with the laser scanning to detect the temperature rise of the joint in response to the laser heating. Properly soldered joints experience a predetermined temperature rise in a given time period. Therefore, solder joints which have temperatures falling outside the specified range for the predetermined period can be identified as defective. In operation, a microprocessor is used to monitor the raster scanning and infrared measurements to record the position and response of the solder joint to the laser and to compare those responses with a stored matrix obtained from a laser scan of a good circuit board. Such a system, however, is extremely expensive and cannot be used in a variety of environments in which inspection may be required.
In still other systems, electronic circuit boards can be excited with conventional test equipment to simulate circuit operation. In such systems, the responses of the circuits to the excitation can then be analyzed in a microprocessor and compared against a standard response for the particular circuit under inspection. In these instances, the microprocessor can also identify, based upon circuit response, the most likely components or connections that may have a defect needing repair. Again, however, such systems are relatively restricted in their applicability and generally costly in their implementation.
Accordingly, the present invention has been developed to overcome the specific shortcomings of the above known and similar techniques and to provide an improved visual inspection system which is easier to use, less costly in implementation, and allows inspection in a variety of different environments.